Clearing specified blocks of main storage

ABSTRACT

Embodiments of the present invention provide systems and methods for clearing specified blocks of main storage. In one embodiment, an EADM start subchannel is executed. The instructions of the execution of the EADM start subchannel may include a SAP receiving an ADM request block, which specifies a main-storage-clearing operation command. The address and size of a block of main memory to be cleared by the SAP is specified in an MSB designated by the ADM request block.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of data processingoperations, and more particularly to clearing operations for specifiedblocks of main storage.

The amount of main memory on a computing device is important because itdetermines how many programs may be executed at one time and how muchdata may be readily available to a program. One known method of clearingstorage is the use of Move Long (MVCL) operation, or analogousoperations Move Long Extended (MVCLE) and Move Long Unicode (MVCLU).Execution of these instructions is synchronously performed by a centralprocessing unit (CPU); however, the execution of these instructions mayreduce the overall throughput of the CPU.

SUMMARY

According to one embodiment of the present invention, a method in a dataprocessing system for clearing blocks of main storage is provided, themethod comprising: determining, by a processor, from an instructionstream, an extended asynchronous data mover (EADM) start subchannelinstruction; and executing, by the processor, the EADM start subchannelinstruction, the executing comprising: notifying, by the processor, asystem assist processor (SAP); receiving, by the SAP, an asynchronousdata mover (ADM) request block; determining, by the SAP, whether the ADMrequest block specifies a main-storage-clearing operation command;responsive to determining the ADM request block specifies themain-storage-clearing operation command, obtaining one or more movespecification blocks (MSBs), wherein an address associated with the oneor more MSBs is designated by the ADM request block; and sending the ADMrequest block; determining, by the SAP, based on the one or more MSBs,an address and a size of a main storage block to clear; and responsiveto determining the address and the size of the main storage block,clearing, by the SAP, the main storage block.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a functional block diagram of a computing environment, inaccordance with an embodiment of the present invention;

FIG. 2 depicts the interrelations of the storage structures used in anEADMF main-storage-clearing operation, in accordance with an embodimentof the present invention;

FIG. 3A depicts a flowchart illustrating operational steps for clearingspecified blocks of main storage, in accordance with an embodiment ofthe present invention; and

FIG. 3B depicts a flowchart illustrating operational steps for anoperating system to monitor the main storage clearing operations of asystem-assist processor (SAP), in accordance with an embodiment of thepresent invention.

DETAILED DESCRIPTION

The growth of cloud computing, analytics, and big data brings anincreased need for efficient processes to control the moving andclearing of data, such as blocks of memory. Embodiments of the presentinvention provide methods and systems for increasing the efficiency ofoperation of a CPU by off-loading the main storage clearing operationsto a separate I/O processor in the data processing environment, such asthe extended asynchronous data mover facility (EADMF).

The present invention will now be described in detail with reference tothe Figures. FIG. 1 depicts a functional block diagram illustrating acomputing environment, generally designated 100, in accordance with anembodiment of the present invention. Modifications to environment 100may be made by those skilled in the art without departing from the scopeof the invention as recited by the claims. In an exemplary embodiment,environment 100 includes I/O devices (i.e., disk drive(s) 150, tapedrives 152, printer(s) or terminal(s) 154, storage-class memory 156, andnetwork adaptor(s) 158) and computing system 110. The I/O devices areconnected to I/O subsystem 120 via I/O device connection 160.

Computing system 110 includes I/O subsystem 120, main memory 130, andCPUs 140A-H, all interconnected by interconnection bus 170. In thisexemplary embodiment, I/O subsystem 120 includes system assistprocessors (SAPs) 122A-D. SAPs 122A-D are each processing units whichrun the channel subsystem to control input/output operations. SAPs122A-D communicate with one or more of CPUs 140A-H by means of a sharedbus, such as interconnection bus 170, and by means of shared structuresin memory. Among other operations, SAPs 122A-D perform memory clearingoperations of main memory 130.

CPUs 140A-H may execute instructions of operating systems (OS) 134A and134B. Operating systems may include the z/OS®, z/VM, z/VSE, zLinux, orTPF operating systems available from International Business Machines ofArmonk, N.Y., or in other embodiments, CPUs 140A-H may executeinstructions of other operating systems. OS 134A and 134B each issuestart subchannel (SSCH) instructions, which are issued by OS 134A and134B to start EADMF operations (discussed further below).

In this exemplary embodiment, main memory 130 is divided into multiplelogical configurations representing virtualized computing systems. Theconfigurations comprise a first level, including logical partitions(LPARs) 132A-B. Each of LPARs 132A and 132B run OS 134A and 134B,respectively, and application program(s) 136A and 136B, respectively. Insome embodiments, main memory 130 may be divided up into logicalconfigurations comprising up to one hundred LPARs. A second level (notdepicted in FIG. 1) represents an operating system, such as z/VM, whichprovides its own second-level configurations. Thousands of virtualmachines may exist under one or more z/VM partitions.

In this exemplary embodiment, CPUs 140A-H and the I/O devices areapportioned to an individual LPAR. For example, CPUs 140A-D may beallocated to LPAR 132A while CPUs 140E-H may be allocated to LPAR 132B.The plurality of I/O devices in FIG. 1 may be apportioned between LPARs132A and 132B in a similar manner as CPUs 140A-H. In other embodiments,CPUs and I/I devices may be shared by one or more LPARs.

FIG. 2 depicts the interrelations of the storage structures used in anEADMF main-storage-clearing operation, in accordance with an embodimentof the present invention. While this embodiment depicts a particular setof fields in each storage structure, in other embodiments, additionalfields may be depicted in each storage structure.

Start subchannel instruction 210 is located in main memory 130 ofoperating system 134A, and is executed by a CPU, such as CPUs 140A-H(not depicted in FIG. 2). In this exemplary embodiment, start subchannelinstruction 210 includes two operands: subsystem ID 211 and EADMoperation request block (ORB) 212. The operand subsystem ID 211designates an asynchronous data mover (ADM) subchannel to be used toperform the clearing operation, while the operand EADM ORB 212designates the address of EADM ORB 220.

In this exemplary embodiment, EADM ORB 220 contains the fields:interruption parameter 221, subchannel key 222, EADM asynchronousoperation block (AOB) address 223, and channel subsystem (CSS) priority224. EADM AOB address 223 identifies the location of EADM AOB 230, whichincludes ADM request block 232, ADM response block 234, and one or moremove specification blocks (MSBs) 240A-N.

In this exemplary embodiment, MSBs 240A-N each contain the fields:format 241, flags 242, block size 243, block count 244, and main memoryaddress 245. Flags 242 contained within MSBs 240A-N may directlydesignate the block of main storage to be cleared (e.g., main memoryblocks 260B and 260E of FIG. 2). The list of block addresses to becleared does not have to be contiguous. For example, one contiguousblock of addresses of storage to be cleared may be specified, or a listof non-contiguous addresses of storage to be cleared may be listed. Ifthe blocks of storage to be transferred for a clear operation are notcontiguous in main storage, a new MSB may be used, or the MSB may useindirect addressing by specifying a list of one or moreasynchronous-indirect-address words (AIDAWs) 250A-N to designate thenon-continuous blocks. In this exemplary embodiment, each of AIDAWs250A-N contain the fields: flags 251 and main memory address 252. Flags251 contained within AIDAWs 250A-N may either directly designate theblock(s) of main memory to be cleared (e.g., main memory blocks 260A,260C, and 260D of FIG. 2), or flags 251 may designate the address ofanother AIDAW so that one or more groups of AIDAWs 250A-N may be linkedtogether. EADM operations, once initiated, are performed by firmwarerunning on a SAP and operate asynchronously from program instructionsthat are executed by a CPU.

As examples to which the invention has particular relevance, see“z/Architecture Principles of Operation,” IBM® Publication No.SA22-7832-09 and U.S. patent application Ser. No. 13/157,729, filed onJun. 10, 2011, which are incorporated herein by reference in theirentirety.

FIG. 3A depicts flowchart 300 illustrating operational steps forclearing specified blocks of main storage, in accordance with anembodiment of the present invention.

In step 302, an I/O start operation is initiated by the CPU, executingan EADM start subchannel instruction issued by operating system 134A(FIG. 2). In this exemplary embodiment, the executed EADM startsubchannel instruction designates an ADM subchannel and an EADM ORB,such as EADM ORB 220.

In step 304, an operand of the EADM start subchannel instruction isreceived, which designates the location of EADM ORB 220 (FIG. 2).

In step 306, the address of EADM AOB 230 to be implemented is obtainedfrom EADM ORB 220. In step 308, one or more available SAPs, such as oneor more of SAPs 122A-D, receives the address of EADM AOB 230, accessesEADM AOB 230, and extracts ADM request block 232. SAPs 122A-D determinewhether ADM request block 232 specifies a main-storage-clearingoperation. ADM request block 232, is obtained from information containedin EADM AOB 230, and one or more MSBs 240A-N are designated, each MSBcontaining information for main-storage-clearing operations.

In step 310, after SAPs 122A-D determine that ADM request block 232specifies a main-storage-clearing operation, SAPs 122A-D perform theactual main-storage-clearing operations, based on the specifications(i.e., address, size, etc.) in MSBs 240A-N associated with ADM requestblock 232. An interruption mechanism is provided to asynchronouslynotify the CPU when a SAP has successfully completed themain-storage-clearing operations. The interruption mechanism is alsoused to report unsuccessful operation completion due to errors in therequest block or MSB format or memory access problems. The error type isspecified in ADM response block 234. After an EADM start subchannelinstruction signals the SAP to begin an EADM main-storage-clearingoperation, processing of the operation by the SAP continues untilcomplete, regardless of the number of MSBs and data blocks specified. Ifa SAP is only allowed a specified time period for task execution,partially completed instructions may be put on a queue by the SAP tocontinue the remaining task execution. A recovery scheme is alsoprovided to ensure instruction completion by either restart orcontinuation, in the event of a SAP failure. In this exemplaryembodiment, the SAP has the same architecture as the CPU on whichoperating systems and application programs execute, and performs memoryclearing operations in a similar manner as a CPU-based clear (i.e., MVC,MVCL, etc.). In this manner, the CPU is free to perform other operationswhile the SAP executes the main storage clearing instructions.

FIG. 3B depicts flowchart 400 illustrating operational steps for anoperating system, such as OS 134A, to monitor the main storage clearingoperations of a SAP, in accordance with an embodiment of the presentinvention.

In step 320, the operating system receives general frequency statisticsassociated with the main-storage-clearing operations of SAPs 122A-D(FIG. 1). For example, the operating system may receive statistics suchas the number of blocks cleared, the number of blocks to be cleared, thesize of the blocks cleared, and the reason for clearing the specifiedblocks, among other information.

In step 322, the operating system determines whether it is mostefficient to use a combination of CPU-based storage clearing operationsand SAP-based storage clearing operations. The operating systemdetermines whether using a combination of CPU and SAP storage clearingoperations is most efficient by analyzing frequency statistics andmetrics, such as latencies involved and the current workload in the CPU,among other data. If the operating system determines that it is mostefficient to use a combination of CPU-based and SAP-based clearingoperations, then, in step 324, the operating system continually analyzesthe frequency statistics of the system to identify a breakpoint from thedata, determining the point at which it is more effective to use the CPUfor storage clearing instructions and at which point it is moreeffective to use the SAP-based main-storage-clearing operations. Theoperating system determines an EADMF subchannel(s) to receive thestorage clear requests, based partially on which subchannel(s) arebetter able to distribute the storage clear requests.

If in step 322, the operating system determines that is not mostefficient to use a combination of CPU-based and SAP-based clearingoperations, then, in step 326, the operating system determines whetherit is more efficient to use the SAP-based storage clearing operationrather than the CPU-based storage clearing operation. As describedabove, the operating system may analyze frequency data obtained, such asthe current workloads on each processor, to determine whether aSAP-based storage clearing operation is more efficient than a CPU-basedclear.

If in step 326, the operating system determines that it is moreefficient to use a SAP-based storage clearing operation than a CPU-basedstorage clearing operation, then, in step 330, the operating systemdetermines an EADMF subchannel(s) to receive the storage clearrequest(s). In this exemplary embodiment, the operating system monitorsthe EADMF main-storage-clearing operations and determines whether theoperations are being effectively serviced on the designatedsubchannel(s). A different subchannel, or multiple subchannels, may beselected to handle the operation request if the operating systemdetermines that the different subchannels are better able to distributethe request.

If in step 326, the operating system determines that it is not moreefficient to use the SAP-based clearing operations rather than theCPU-based clearing operations, then, in step 328, only the CPU executesthe storage clearing instructions.

The operating system will continually perform the operational steps ofFIG. 3B to examine various metrics about the CPU-based and SAP-basedstorage clearing operations, and to ensure that the EADMmain-storage-clearing operations are being executed in an optimizedmanner.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The terminology used herein was chosen to best explain the principles ofthe embodiment, the practical application or technical improvement overtechnologies found in the marketplace, or to enable others of ordinaryskill in the art to understand the embodiments disclosed herein.

What is claimed is:
 1. A method in a data processing system comprising:determining, by a processor, from an instruction stream, an extendedasynchronous data mover (EADM) start subchannel instruction; executing,by the processor, the EADM start subchannel instruction, wherein theexecuting comprises notifying a system assist processor (SAP);receiving, by the SAP, an asynchronous data mover (ADM) request block;determining, by the SAP, whether the ADM request block specifies amain-storage-clearing operation command; responsive to determining theADM request block specifies the main-storage-clearing operation command,obtaining one or more move specification blocks (MSBs), wherein anaddress associated with the one or more MSBs is designated by the ADMrequest block; determining, by the SAP, based on the one or more MSBs,an address and a size of a main storage block to clear; and responsiveto determining the address and the size of the main storage block,clearing, by the SAP, the main storage block.
 2. The method of claim 1,further comprising: receiving, by an operating system, results of themain-storage-clearing operation command; determining, by the processor,whether the main-storage-clearing operation command completedsuccessfully; and responsive to determining that themain-storage-clearing operation command completed successfully,reporting one or more SAP resources used to complete the command.
 3. Themethod of claim 2, further comprising: responsive to determining thatthe main-storage-clearing operation command did not completesuccessfully, providing an indication of an error associated with an MSBand an asynchronous-indirect-address-word (AIDAW).
 4. The method ofclaim 1, wherein the main-storage-clearing operation command operatesasynchronously from a program on a CPU.
 5. The method of claim 1,further comprising: specifying, by the one or more MSBs, a first AIDAWaddress; obtaining the first AIDAW address; determining, by one or moreflags associated with an AIDAW, an address of a main storage block toclear, wherein a size of the main storage block to clear is determinedby the one or more MSBs; and responsive to determining by the one ormore flags associated with the AIDAW the address of the main storageblock to clear, clearing the main storage block.
 6. The method of claim5, further comprising: determining, by the one or more flags associatedwith the first AIDAW address, a second AIDAW address; and responsive todetermining the second AIDAW address, obtaining, one or more groupingsof AIDAWs, wherein the one or more groupings of AIDAWs are linked. 7.The method of claim 1, wherein an operating system determines an EADMFsubchannel to service the main-storage-clearing operation command, andwherein a determination of the EADMF subchannel is based, at least inpart, on a workload associated with the EADMF subchannel.
 8. A computerprogram product comprising: a computer readable storage medium andprogram instructions stored on the computer readable storage medium, theprogram instructions comprising: program instructions to determine, by aprocessor, from an instruction stream, an EADM start subchannelinstruction; program instructions to execute, by the processor, the EADMstart subchannel instruction, the program instructions to executecomprising program instructions to notify a SAP; program instructions toreceive, by the SAP, an ADM request block; program instructions todetermine, by the SAP, whether the ADM request block specifies amain-storage-clearing operation command; program instructions to,responsive to determining the ADM request block specifies amain-storage-clearing operation command, obtain one or more MSBs,wherein an address associated with the one or more MSBs is designated bythe ADM request block; program instructions to determine, by the SAP,based on the one or more MSBs, an address and a size of a main storageblock to clear; and program instructions to, responsive to determiningthe address and the size of the main storage block, clear, by the SAP,the main storage block.
 9. The computer program product of claim 8,further comprising: program instructions to receive, by an operatingsystem, results of the main-storage-clearing operation command; programinstructions to determine, by the processor, whether themain-storage-clearing operation command completed successfully; andprogram instructions to, responsive to determining that themain-storage-clearing operation command completed successfully, reportone or more SAP resources used to complete the command.
 10. The computerprogram product of claim 9, further comprising: program instructions to,responsive to determining that the main-storage-clearing operationcommand did not complete successfully, provide an indication of an errorassociated with an MSB and an AIDAW.
 11. The computer program product ofclaim 8, wherein the main-storage-clearing operation command operatesasynchronously from a program on a CPU.
 12. The computer program productof claim 8, further comprising: program instructions to specify, by theone or more MSBs, a first AIDAW address; program instructions to obtainthe first AIDAW address; program instructions to determine by one ormore flags associated with an AIDAW, an address of a main storage blockto clear, wherein a size of the main storage block to clear isdetermined by the one or more MSBs; and program instructions to,responsive to determining by the one or more flags associated with theAIDAW the address of the main storage block to clear, clear the mainstorage block.
 13. The computer program product of claim 12, furthercomprising: program instructions to determine, by one or more flagsassociated with the first AIDAW address, a second AIDAW address; andprogram instructions to, responsive to determining the second AIDAWaddress, obtain one or more groupings of AIDAWs, wherein the one or moregroupings of AIDAWs are linked.
 14. The computer program product ofclaim 8, wherein an operating system determines an EADMF subchannel toservice the main-storage-clearing operation command, and wherein adetermination of the EADMF subchannel is based, at least in part, on aworkload associated with the EADMF subchannel.
 15. A computer systemcomprising: one or more computer processors; one or more computerreadable storage media; program instructions stored on the one or morecomputer readable storage media for execution by at least one of the oneor more processors, the program instructions comprising: programinstructions to determine, by a processor, from an instruction stream,an EADM start subchannel instruction; program instructions to execute,by the processor, the EADM start subchannel instruction, the programinstructions to execute comprising program instructions to notify a SAP;program instructions to receive, by the SAP, an ADM request block;program instructions to determine, by the SAP, whether the ADM requestblock specifies a main-storage-clearing operation command; programinstructions to, responsive to determining the ADM request blockspecifies a main-storage-clearing operation command, obtain one or moreMSBs, wherein an address associated with the one or more MSBs isdesignated by the ADM request block; program instructions to determine,by the SAP, based on the one or more MSBs, an address and a size of amain storage block to clear; and program instructions to, responsive todetermining the address and the size of the main storage block, clear,by the SAP, the main storage block.
 16. The computer system of claim 15,further comprising: program instructions to receive, by an operatingsystem, results of the main-storage-clearing operation command; programinstructions to determine, by the processor, whether themain-storage-clearing operation command completed successfully; andprogram instructions to, responsive to determining that themain-storage-clearing operation command completed successfully, reportone or more SAP resources used to complete the command.
 17. The computersystem of claim 16, further comprising: program instructions to,responsive to determining that the main-storage-clearing operationcommand did not complete successfully, provide an indication of an errorassociated with an MSB and an AIDAW.
 18. The computer system of claim15, further comprising: program instructions to specify, by the one ormore MSBs, a first AIDAW address; program instructions to obtain thefirst AIDAW address; program instructions to determine by one or moreflags associated with an AIDAW, an address of a main storage block toclear, wherein a size of the main storage block to clear is determinedby the one or more MSBs; and program instructions to, responsive todetermining by the one or more flags associated with the AIDAW theaddress of the main storage block to clear, clear the main storageblock.
 19. The computer system of claim 18, further comprising: programinstructions to determine, by one or more flags associated with thefirst AIDAW address, a second AIDAW address; and program instructionsto, responsive to determining the second AIDAW address, obtain one ormore groupings of AIDAWs, wherein the one or more groupings of AIDAWsare linked.
 20. The computer system of claim 15, wherein an operatingsystem determines an EADMF subchannel to service themain-storage-clearing operation command, and wherein a determination ofthe EADMF subchannel is based, at least in part, on a workloadassociated with the EADMF subchannel.